Manufacture of non-CFC cellular resol foams using perfluorinated ethers

ABSTRACT

The invention relates to a process for producing non-CFC resol foams of low density using perfluorinated ethers along with a HCFC or CFC blowing agent, and to foams produced by such a process. The process generally comprises: (a) forming a mixture by combining a resol resin with a blowing-agent blend comprising (i) at least one blowing agent selected from the group consisting of hydrogenated chlorofluorocarbons and hydrogenated fluorocarbons and (ii) at least one perfluoroether additive selected from the group consisting of perfluorinated ethers; (b) adding an acid catalyst to the mixture to initiate foaming and form a foam; and (c) curing the foam to form a cured foam that is essentially free of CFCs.

CROSS-REFERENCE TO RELATED APPLICATION

This is a division of U.S. patent application Ser. No. 08/734,947, filedOct. 22, 1996.

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION

The present invention generally relates to processes of manufacturingnon-CFC cellular resol foams of low density using a blowing-agent blendcontaining perfluorinated ethers. The invention further relates to foamsproduced using blowing-agent blends containing HCFC and/or HFC blowingagent(s) and perfluorinated ether(s).

The foams of the present invention are useful in a wide variety ofinsulating applications. Applications include use in making productsfrom commercial roofing insulation and industrial cavity walls toresidential sheathing for walls.

BACKGROUND OF THE INVENTION

Cellular foams have long been produced using chlorofluorocarbon (CFC)blowing agents. More recently, the industry has been attempting to phaseout the use of ozone depleting substances such as CFCs in the productionof foams. In this effort to minimize the effect on the environment, theindustry has moved toward the use of hydrogenated chlorofluorocarbons(HCFCs) and hydrogenated fluorocarbons (HFCs) as blowing agents. Forexample, U.S. Pat. Nos. 5,489,619, 5,407,963 and 5,441,992 describemethods for producing non-CFC foams.

However, the use of HCFCs and HFCs in place of CFCs has resulted in anumber of problems. Due to the high solvency (i.e., ability tosolubilize resin or act as a solvent for resin) of some of these blowingagents, the resulting foams tend to have a larger cell size, which canhave a negative impact on both thermal and mechanical properties of thefoam. Furthermore, some of the less ozone-depleting blowing agents aregases at room temperature. Therefore, producing foams with these blowingagents can present a challenge particularly for some of the very lowboiling blowing agents, where controlling the rate of expansion can bedifficult.

While aiming to prepare foams using more environmentally friendlyblowing agents, the industry has been striving to produce foams wit hbetter performance characteristics. Unfortunately, advances in reducingenvironmental impact have been accompanied by losses in the propertiesof the resulting foam. This was typically because the lessozone-depleting alternatives were more soluble than CFCs and resulted infoams having larger cell sizes with inferior thermal and mechanicalproperties. To date, substitutes are still sought that will avoidenvironmental concerns associated with the use of CFCs while essentiallymaintaining the foam mechanical and thermal properties. A blowing-agentsystem that is less harmful to the environment in addition to providingmaintained or improved product performance is highly desired.

SUMMARY OF THE INVENTION

Accordingly, one object of the invention is to achieve anenvironmentally friendly process for producing resol foams havingadvantageous properties. These and other objects and advantages ofinvention, which will become apparent from the foregoing and thedetailed description below, have been attained by the present invention.

We have discovered that the addition of perfluorinated ethers to HCFCand/or HFC blowing agents surprisingly improves the properties of resolfoams. Not only do the perfluoroether (PFEs), when added in quantitiesof from about 1 to about 3 percent by weight based on the weight of theblowing agent, result in a foam with improved thermal performance andfriability compared to foams made without the PFE additive, but theaddition of the PFE to the foaming system improves the processability ofthe foam. In particular, improvements in processability include bettercontrol of wetness at the froth dispensed from the mix. The resultingPFE-blown foam typically is of a lower density with equivalent orimproved properties over those of a non-PFE blown foam. The presentinvention therefore provides for the production of a low-densitycellular foam with improved or preserved thermal and mechanicalproperties and with minimal negative impact on the environment.

Thus, one aspect of the present invention relates to a method or processfor producing a closed-cell non-CFC resol phenolic foam using blowingagents. The process includes the steps of: (a) adding to a resol resin ablowing-agent blend comprising (1) one or more hydrogenatedchlorofluorocarbons or hydrogenated fluorocarbons and (2) one or moreperfluorinated ethers (perfluoroether); (b) adding an acid catalyst toinitiate foaming of the blend and produce a foam; and (c) curing thefoam. In another aspect, the invention relates to a blowing-agent blendcomprising: (a) one or more members selected from hydrogenatedchlorofluorocarbons and hydrogenated fluorocarbons; and (b) one or moreperfluoroether. The blowing-agent blend preferably contains theperfluorinated ether(s) in a total amount of from about 1% to about 3%by weight based on the total weight of the blowing-agent blend (PFE andHCFC and/or HFC blowing-agent components). More preferably, theperfluorinated ethers are present in an amount of from 2 to 3 percent byweight, based on the total weight of the blend components. The inventionfurther relates to foams produced via the processes of the invention.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a diagram illustrating how foam-cell height is determined.As depicted in the FIGURE, the cell height is based on the longeststraight distance parallel to the direction of heat flow from one cellwall to the opposite cell wall.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS OF THE INVENTION

A closed-cell resol foam may be prepared using CFC-free blowing agentsby steps including the following: (a) adding to a resol resin ablowing-agent blend essentially free of CFCs comprising (1) one or morehydrogenated chlorofluorocarbons or hydrogenated fluorocarbons and (2)one or more perfluorinated ethers (perfluoroether); (b) adding an acidcatalyst to initiate foaming of the blend and produce a foam; and (c)curing the foam. In a preferred embodiment, the blowing-agent blendconsists essentially of: (a) one or more members selected fromhydrogenated chlorofluorocarbons and hydrogenated fluorocarbons; and (b)one or more perfluoroether.

Preferably, the HCFCs or HFCs used in the blends have low boilingpoints-in particular, boiling points below about 0° C. Exemplary lowboiling-point HCFC or CFC blowing agents preferably used in the blendsinclude 1-chloro-1,1-difluoroethane ("142b"), chlorodifluoro-methane("22"), 2-chloro-1,1,1,2-tetrafluoroethane ("124"), 1,1-difluoroethane("152a"), pentafluoroethane ("125") and 1,1,1,2-tetrafluoroethane("134a"). In addition, the HCFCs and HFCs preferably have low thermalconductivities as gases. It is also preferred that the HCFCs and HFCshave low solvencies.

Preferred perfluorinated ethers are those represented by the generalformula: ##STR1## In the above formula, n is an integer of from 0 to 3and m is an integer of from 0 to 1.

Specific examples of preferred perfluorinated ethers includepolymerized, oxidized 1,1,2,3,3-hexafluoro-propene, e.g., "Galden HT-55"and "Galden HT-70" (available from Ausimont SpA and Ausimont USA), whichhave typical properties (measured at 25° C.) as shown in the followingchart:

    ______________________________________                                        Typical Properties                                                                        HT55     HT70      Units                                          ______________________________________                                        Boiling Point                                                                             55       70        °C.                                     Pour Point  *        -115      °C.                                     Density     1.67     1.68      g/gm.sup.3                                     Kinematic Viscosity                                                                        .45     0.60      cst                                            Vapor Pressure                                                                            228      165       Torr                                           Specific Heat                                                                             *        0.23      --                                             Heat of Vaporization                                                                      *        17        cal/g                                          Thermal Conductivity                                                                      *        0.0007    W/(cm)(°C.)                             Coeff. of Expansion                                                                       *        0.0011    cm.sup.3 /(cm.sup.3).sup.( °C.)         Surface Tension                                                                           *        14        dynes/cm                                       Refractive Index                                                                          *        1.280     --                                             Dielectric Strength                                                                       *        40        kV (2.54 mm gap)                               Dielectric Constant                                                                       *        2.1       (1 kHz)                                        Dissipation Factor                                                                        *        2 × 10.sup.4                                                                      (1 kHz)                                        Volume Resistivity                                                                        *        1 × 10.sup.15                                                                     ohm-cm                                         Solubility of water                                                                       *        14        ppm (wt.)                                      Solubility of Air                                                                         *        26        cm.sup.3 gas/100 cm.sup.3 liquid               Molecular Weight                                                                          *        410       --                                             ______________________________________                                         *Nonspecified properties should be similar to those for HT70, except that     vapor pressure for HT55 will be higher and pour point will be lower.     

The blowing-agent blend preferably contains the perfluorinated ether(s)in a total amount of from 1% to 3% by weight based on the total weightof the blend (PFE and HCFC and/or HFC blowing-agent components). Morepreferably, the perfluorinated ethers are present in a total amount offrom 2 to 3 percent by weight based on the total weight of the blendcomponents.

The acid catalyst may be a single catalyst or a blend of catalysts.Preferred catalysts are sulphonic acids, e.g., xylene and toluenesulphonic acids

Optional ingredients may be added, either separately or in a system orblend along with another ingredient such as the acid catalyst. Forexample, urea may be added as a formaldehyde scavenger. Other optionalmodifiers such as resorcinol and diethylene glycol may be added, e.g.,as taught in U.S. Pat. Nos. 4,883,824 and 4,945,077, the disclosures ofwhich are incorporated by reference herein. For instance, a catalystsystem containing one or more acid catalysts may be prepared bypreblending the resorcinol and glycol and then combining them with theacid catalyst(s) or by preblending the acid catalyst(s) and glycol andthen combining the preblend with resorcinol.

The non-CFC resol foams produced according to the invention preferablyhave a density of from 0.5 to 3.0 pcf (pounds per cubic foot), morepreferably from 0.8 to 2.8 pcf. Such foams are particularly advantageousfor use as insulating materials.

Foams may be prepared from resol resins or resin systems using theblowing-agent blends of the present invention by basic steps including(a) preparing the resol resin, (b) adding the blowing-agent blend (andany optional ingredients) to the resin to prepare a resol mixture, (c)adding the catalyst system (with or without optional ingredients) andfoaming the mixture to produce a foam, and (d) curing the foam.

Preferably, the resol resin is prepared as follows. Phenol andformaldehyde are combined at a conventional starting molar ratio ofphenol to formaldehyde-here, preferably using a molar ratio of from 1:1to 1:4.5 phenol to formaldehyde, more preferably from 1:1.5 to 2.5. Thehigh molar ratios of formaldehyde provides resins that are substantiallyfree of phenol and that can be treated with a formaldehyde co-reactantor scavenger to reduce the initially high free-formaldehyde content.Modifying agents, such as melamine, resorcinol and/or urea, arepreferably added; urea is an especially preferred modifying agent. Theresin is then neutralized with 50% aqueous aromatic sulphonic acid. Theresin is passed through a thin-film evaporator to reduce the free-watercontent. After the resin exits the thin-film evaporator, surfactant isadded to the resin, preferably as described in U.S. Pat. No. 5,407,963,the disclosure of which is incorporated by reference herein. The amountand type of surfactant is suitably selected to obtain the desired cellstructure (closed-cell content and cell size). Preferred surfactants areethylene-oxide based nonionic surfactants, such as Pluronic F127(available from BASF). Blends of surfactants, such as a 1/1 w/w blend ofPluronic F127 and Harfoam PI (available from Huntsman Chemical), mayalso be used.

A typical resin used for manufacturing resol foam has a viscosity on theorder of from 5,000 to 40,000 cps at 40° C. and has a free-water contentof 4-8%. In manufacturing phenolic foams from high-viscosity resins inaccordance with the present invention, the resin utilized preferably hasa viscosity on the order of from 7,000 to 20,000 cps at 40° C.

The blowing-agent blend is prepared in a suitable manner. For example,PFE is combined in a pressure vessel with an HCFC and/or HFC blowingagent. The blend is then mixed, e.g., by sparging. The blowing-agentblend is combined with the resol resin, e.g., by metering theseingredients to a mixer, which is preferably a high-shear,short-residence rotor/stator continuous mixing device.

To initiate foaming, the acid catalyst is added to the mixer along withthe resol resin and blowing-agent blend, as well as any optionalingredients, while the combination is mixed. For example, a Micromotionmass-flow metering device may be used to deliver the blowing agent andcatalyst, and a metering pump may be used to deliver the resin. Optionalingredients may be added in a variety of ways--e.g., a preblend ofresorcinol and diethylene glycol may be combined with the acid-catalystsystem (one or more acid catalysts), or a preblend of an acid catalystand diethylene glycol may be combined with resorcinol.

It is important that the pressure inside the mixer be controlled towithin a range that prevents premature foaming, typically a pressure offrom 170 to 250 psig. The specific pressure range depends on the vaporpressure and boiling point of the blowing agent and on the temperatureof the mixture in the mixer. A low-boiling blowing agent like HCFC 142b,which has a boiling point of -9.8° C. requires pressures in the foammixer to be sufficiently high to prevent premature foaming.

The resulting thermosetting foam is cured. Preferably, foam is cured byconveying through a conveyor oven at a temperature of from about 60 to95° C. more preferably of about 80° C. at a fixed rate sufficient toproduce a board that is cured enough to handle. Preferably, preparationof the foams of the present invention further involves a rampingpostcure procedure as follows: 0 to 70 minutes at 75°-85° C.; followedby 20 to 105 minutes at 90°-95° C.; followed by 60 to 170 minutes at100°-105° C. The ramped postcure cycle can reduce the cell-wall damagethat might otherwise occur to the foam if it were to be postcured underhigher initial temperatures, while reducing the postcure time bygradually increasing the curing temperature, and therefore rate of cure,instead of maintaining the temperature at the relatively low initialtemperature. The low initial postcure temperature and the ramping cyclehelp ensure that the green foam is not exposed to high temperatures whenthe foam cell walls are still weak and undercured. The rampingtemperature cycle also allows the foam cell walls to cure and strengthenat a more controlled rate, with a gradual elimination of the water vaporproduced during the curing reaction. A foam may thus be produced thatadvantageously can withstand increased internal cell pressure and resistcell rupture at higher temperatures. A ramped postcure cycle can alsoreduce cell wall damage that would occur under more severe constanttemperature postcure conditions, such as immediate exposure to atemperature greater than 100° C., and can improve the thermalperformance of the foam.

The invention will now be further described in reference to thefollowing nonlimiting examples.

EXAMPLE 1 Preparation of Resol Resin

A resol resin used to produce foams as described below was preparedusing a formaldehyde:phenol (F/P) mole ratio of 2.3:1, usingformaldehyde (52% by weight of aqueous solution) and phenol (99%purity). The reaction was carried out under basic conditions (using 50%by weight sodium hydroxide solution) at elevated temperatures. When theOstwald viscosity of the resin reached 62 cst (centistokes) as measuredat 62° C., the reaction mixture was cooled and then neutralized with 50%by weight aqueous aromatic sulphonic acid. Urea was added as aformaldehyde scavenger at a level of 77% by mole of the residualformaldehyde. The resin was passed through a thin-film evaporator toreduce the water content from about 30% to 4-7% by weight. An ethyleneoxide based nonionic surfactant (Pluronic F127 or a 1/1 w/w blend ofPluronic F127F and Harfoam PI) was then added at 3.5% by weight of theresin and mixed into the resin to form a homogenous blend. The finalviscosity of the resin was 8000-12000 cps (centipoise) as measured at40° C.

COMPARATIVE EXAMPLE 2 Preparation of Foam Using HCFC 142b

A non-CFC resol foam was prepared by mixing together the resol resin andsurfactant of Example 1 with HCFC 142b blowing agent and an acidcatalyst while mixing using a high-shear, short-residence rotor/statorcontinuous mixer. The HCFC 142b blowing agent was saturated withnitrogen at 200 psi (pounds per square inch) prior to introduction intothe mixture. The catalyst system for initiating foaming was acombination of xylene and toluene sulphonic acids blended withresorcinol and diethylene glycol, as described in U.S. Pat. Nos.4,883,824 and 4,945,077. The resol resin, blowing agent and catalystsystem were continuously metered to the mixer by means of suitableflow-metering devices (Micromotion metering device for the blowing agentand catalyst blend, and a metering pump for the resin) in the followingweight ratios:

    ______________________________________                                        resin + surfactant                                                                            100.00                                                        HCFC 142b       7.43                                                          catalyst system 11.15                                                         ______________________________________                                    

The pressure inside the mixer was controlled to within a range of from170 to 250 psig. The foamable mixture (resin/surfactant, blowing-agentblend, catalyst) exited the mixer through evenly spaced tubes andnozzles to form continuous beads of froth on a moving facer. Thisresulted in parallel lines of foam which knitted together as the frothexpanded, to form a continuous sheet. The foam sheet was then cured byconveying through a conveyor oven at approximately 80° C. at a fixedrate to produce a board that was cured enough to handle. The boards werefurther cured for an additional 3-5 hours at 90°-105° C. to give thefinal product. The curing was as taught in U.S. Pat. No. 5,441,992, thedisclosure of which is incorporated by reference. The resulting foam wasthen tested; the resulting properties are shown in Table 2.

EXAMPLES 3 AND 4 Preparation of Foams Using Blowing-Agent Blends

Following the procedure set forth in Example 2, non-CFC resol foams wereprepared using PFEs as a blowing-agent additive using the componentsshown in Table 1. The perfluoroether additives used in these exampleswere fluids supplied by Ausimont USA having the tradenames "Galden HT55"and "Galden HT70", which are both polyethers. In Examples 3 and 4 apreweighed quantity of PFE was blown with nitrogen into the bottom of anenclosed pressure vessel containing HCFC 142b. This 142b/PFE blend wasthen saturated with nitrogen to 200 psi. This saturation or spargingprocess created enough turbulence to mix the blowing agent and PFEtogether such that no additional mechanical mixing was required. Theresulting foams were tested, with the results summarized in the tablesbelow.

The effect PFE on HCFC 142b-blown resol foams is reflected by theresults from Comparative Example 2 and Examples 3 and 4 given Tables1and 2:

                  TABLE 1                                                         ______________________________________                                        Resol Foam Formulations                                                                              Blowing Agent                                                                            Catalyst                                    Examples Type of PFE.sup. 1!                                                                         (pph).sup. 2!                                                                            (pph).sup. 3!                               ______________________________________                                        2        none used      7.43      11.15                                       3        HT-55         11.30      11.80                                       4        HT-70         11.50      11.90                                       ______________________________________                                         .sup. 1! PFE was added in Exs. 3 and 4 at 2% by weight of the blowing         agent blend.                                                                  .sup. 2! Quantity of blowing agent, measured in parts per hundred parts o     resin by weight (pph), includes the amount of PFE.                            .sup. 3! Quantity of catalyst is given in parts per hundred parts of          resin.                                                                   

                  TABLE 2                                                         ______________________________________                                        Resol Foam Properties                                                               Den-   Thermal     Com-                                                 Ex-   sity   Conductivity                                                                              pressive                                                                             Friability.sup. 5!                                                                    Cell Size                             ample (pcf)  (BTU in/ft.sup.2 hr F.)                                                                   Strength.sup. 4!                                                                     (% wt. Loss)                                                                          (microns)                             ______________________________________                                        2     2.50   0.130       201    23      130                                   3     2.07   0.126       168    17      135                                   4     1.93   0.126       175    17      127                                   ______________________________________                                         .sup. 4! Compressive strength at 10% deformation.                             .sup. 5! Friability tested according to ASTM C421                        

Scanning electron microscopy (SEM) was used to perform foam-cell heightdistribution measurements. SEM was used for analysis of the cell heightand to observe characteristics of the foam's struts, walls, windows andgeneral formation.

The method of analysis used a section of foam cut parallel to themachine direction from the center of a laydown bead. This section wasthen snapped to reveal the cellular structure in the direction of heattransmission from the bottom to the top surface. The resultant surfacewas then prepared for SEM viewing. The SEM micrograph samples were takenfrom the central region of the prepared samples, and the cell heightmeasurements started at the center and proceeded upwards towards the topsurface until 100 counts had been obtained. The location of measurementfor the cell's height was the longest vertical line passing through thecell and is shown in the drawing FIGURE.

Even with a density reduction of about 25% in the PFE-containing foam,the thermal conductivity improved. To quantify the effect of blowingagent and formulation changes on foam brittleness, friability wasmeasured according to ASTM Method C421 and was reported as weight lossas a percent of the whole. The objective was to produce a foam with alow friability. The addition of PFE to HCFC 142b reduced the friabilityby 25%, which is significant given that a density reduction alone cancause an increase in friability. Cell size was similar in the threeexamples. The reduction in compressive strength corresponds to thedensity reduction in Examples 3 and 4.

Further embodiments and modifications of the invention will be apparentthrough practice of the invention in light of the foregoing description.Thus, the invention is intended not to be limited by the above detaileddiscussion, but to be defined by the appended claims and theirequivalents.

What is claimed is:
 1. A CFC-free foam prepared by the processcomprising the steps of:(a) forming a mixture by combining a resol resinwith a blowing-agent blend comprising (i) at least one blowing agentselected from the group consisting of hydrogenated chlorofluorocarbonsand hydrogenated fluorocarbons and (ii) at least one perfluoroetheradditive selected from the group consisting of perfluorinated ethers;(b) adding an acid catalyst to the mixture to initiate foaming and forma foam; and (c) curing the foam to form a cured foam that is essentiallyfree of CFCs.
 2. A foam according to claim 1, wherein the resol resin isprepared by a method comprising reacting phenol with formaldehyde at amolar ratio of from 1:1 to 1:4.5.
 3. A foam according to claim 1,wherein the resol resin has a viscosity at 40° C. of from 7,000 to20,000 centipoise.
 4. A foam according to claim 1, further comprisingadding to the resol resin at least one modifying agent selected from thegroup consisting of urea, resorcinol, and melamine.
 5. A foam accordingto claim 1, further comprising the step of:(d) postcuring the cured foamusing a ramping procedure comprising subjecting the cured foam: for atime of from 0 to 70 minutes to a temperature of from 75° to 85° C.,then for a time of from 20 to 105 minutes to a temperature of from 90°to 95° C., and then for a time of from 60 to 170 minutes to atemperature of from 100° to 105° C.